A Study of Pembrolizumab and Ablation (Cryoablation or Histotripsy) in People With Breast Cancer

This study combines pembrolizumab (an immunotherapy) with cryoablation — a procedure where a tumor is frozen and destroyed with extreme cold — in people with metastatic triple-negative breast cancer (TNBC). The idea is that destroying one tumor with freezing releases signals that may help the immune system attack other cancer sites in the body. **You may be eligible if...** - You are 18 or older - You have confirmed metastatic triple-negative breast cancer (a type that is estrogen receptor-negative, progesterone receptor-negative, and HER2-negative) - You have at least one tumor site that can be safely targeted by cryoablation (at least 1.5 cm in size) - An interventional radiologist has confirmed the procedure is feasible for you - You are physically fit to undergo the cryoablation procedure - Women of childbearing age must use effective contraception during and after treatment **You may NOT be eligible if...** - You have received prior treatment with pembrolizumab or similar checkpoint immunotherapy drugs - No tumor site is accessible or large enough for cryoablation - You have active autoimmune disease - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.